Hecho matemático: 83721 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 83721 is an uninteresting number.
Fecha histórica: March 21st is the day in 1935 that Shah Reza Pahlavi formally asks the international community to call Persia by its native name, Iran, which means 'Land of the Aryans.